Dilce de Fatima Rossetti

A porção sul da Bacia sedimentar intracratônica do Paraná carece de estudos que considerem a possível influência de atividade tectônica na evolução do relevo após o Cretáceo. Este trabalho visa hierarquizar morfoestruturas na porção sul da Bacia do Paraná, abrangendo as Formações Tupanciretã e Serra Geral, com base em topologia de redes de drenagem e lineamentos morfoestruturais. O estudo é desenvolvido com o uso de dados de sensoriamento remoto, incluindo: modelo digital de elevação (MDE) World 3D30 (AW3D30), adquiridos a bordo do Advanced Land Observing Satellite (ALOS); imagens do Satélite Sentinel-2, sensor MSI (MultiSpectral Instrument); e imagens do veículo aéreo remotamente pilotado (VARP) Phantom 4 PRO. As informações obtidas desses produtos foram integradas com dados morfológicos coletados em campo, bem como com a base cartográfica oficial do Estado do Rio Grande do Sul em escala de 1:25.000. O resultado da análise morfoestrutural revelou relevo com indícios de deformação tectônica, registrada por inúmeras anomalias, com destaque para: padrões de drenagem anômalos, como o treliça e subtipos; inflexões abruptas de canais formando ângulos de 90º; e lineamentos morfoestruturais. Duas fases deformacionais principais foram hierarquizadas: a primeira de direção NE-SW, compatível com estruturas tectônicas do Cenozoico Inferior da Bacia do Paraná; e a segunda de direção E-W, concordante com estruturas transcorrentes do Cenozoico Superior, formadas durante a abertura do Oceano Atlântico Sul. Além disso, ocorrem lineamentos morfoestruturais de direção N-S, que foram relacionados com compressão decorrente da colisão das placas de Nazca e Sulamericana.

In intracratonic South America, the origin of neotectonic activity and its impact on large Amazonian rivers have been of continuous research interest, but the available evidence has been only for extensional structures. This investigation focuses on a megascale (~60,000 km2) domal relief from central Amazonia (the Juruá dome). The main goal was to verify the relationship of this anomalous relief with a growing fold and determine the origin of the stress field within the context of Andean uplift along with the westward movement of the South American plate. The approach applied here is unprecedented for the Amazon lowlands. This is because it combines evidence of tectonic adjustments of river systems using morphostructural and morphometric analyses from remote sensing imagery, integrated with subsurface data consisting of gravity and magnetic maps, seismic reflection, and well logs. The Juruá dome consists of a broad, rounded, and smooth, convex relief, with altitudes generally not exceeding 110 m developed into Pleistocene-Holocene deposits. The drainage over the dome is arranged concentrically into a broad annular pattern with localized anomalous segments in the Solimões River and various Amazonian tributaries. The results revealed that the Juruá dome evidence the growth of a broad anticline. Non-linear slightly convex χ-profiles of many rivers that cross or contour the dome evidence transient rivers, consistent with a development under growth fold. The fold modified the course of several rivers within the domal relief area, including the Juruá River, which is entrenched along NE-striking faults that released the stress along the fold axis. NE- and NW-striking normal and reverse faults with flower structure geometries are abundant in subsurface and suggest deformation from strike-slip tectonics. Gravity and magnetic data revealed that the fold and many of its associated faults are deep-rooted into basement rocks. The geomorphological and structural data are collectively compatible with a long-term NW-trending maximum horizontal compressive stress-field that is driving basin inversion. This neotectonic activity can be linked to far-field stresses from the pushes from the Andean orogeny and the movement of the South American plate against the North Andean and Nazca plates. Thus, this study can expand our knowledge on the impact of far-field stresses in intracratonic settings transmitted from collisional and constructional tectonic plates. Detecting active folded reliefs in central Amazonia is a new approach that can help characterize the extension and source of compressive far-field stresses in intracratonic northern South America.

Relative sea-level (RSL) rise associated with decreased fluvial sediment discharge and increased hurricane activity have contributed to the high rate of shoreline retreat and threatened coastal ecosystems in Port Fourchon, Louisiana, USA. This study, based on QuickBird/drone images (2004–2019) and LIDAR data (1998–2013), analyzed the impacts of shoreline dynamics on mangroves (Avicennia germinans) and marshes before and after the initiation of a beach nourishment project in 2013. The coastal barrier and dune crest migrated landward between 1998 and 2013. Meanwhile, the dune crest height increased between 1998 and 2001, then decreased in 2013, probably due to hurricane impacts. The total sediment volume along this sandy coastal barrier presented an overall trend of decline in the 1998–2013 period, resulting in a wetlands loss of ~15.6 ha along 4 km of coastline. This has led to a landward sand migration onto muddy tidal flats occupied by Avicennia germinans (1.08 ha) and Spartina (14.52 ha). However, the beach nourishment project resulted in the advancement of the beach barrier from Nov/2012 to Jan/2015, followed by a relatively stable period between Jan/2015 and Mar/2019. Additionally, both the dune crest height and sediment volume increased between 2013 and 2019. This set of factors favored the establishment and expansion of mangroves (3.2 ha) and saltmarshes (25.4 ha) along the backbarrier environments after 2013, allowing the tidal flats to keep pace with the RSL rise. However, waves and currents caused shoreline erosion following the beach nourishment project between Oct/2017 and Nov/2019, threatening wetlands by resuming the long-term process of shoreline retreat.

Documenting neotectonic instabilities and determining the style and time of deformation in the vast and difficult to access central Amazonia region is challenging. We focus on these issues by investigating a large area of the Negro River drainage basin, applying morphostructural analysis based on synthetic aperture radar data. The digital elevation models of the C-band Shuttle Radar Topography Mission and the L-band Protection System of Amazonia were used as the database. We also used subsurface magnetic information from the Earth Magnetic Anomaly Grid global model to validate the morphostructures. The results revealed NW-oriented morphostructural lineaments bounding multiple depositional valley fills. These were extensively fragmented to form regularly distributed en échelon rectangular blocks commonly offset horizontally by several kilometers. Strike-slip faults and oblique, either normal or reverse, faults are present. These structures were reactivated along the main NE- and SW-oriented regional structural trends due to N-S-oriented horizontal compression and E-W-oriented horizontal extension in the late Pleistocene and Holocene. The extensive neotectonic faulting results from the interplay of plate motion and Andean uplifting since the late Pleistocene, combined with local stresses.

The influence of neotectonic structures on the development of large river valleys is an issue that needs further investigation in various geological settings. Despite the typical low topography, the relief of many areas in central Amazonia was shaped by fault reactivation, but folds have also recently been argued. This work aims to analyze active folding in central Amazonia, determine the regional extent and origin of the compressive stress, and then discuss its control on the development of some large Amazonian rivers. The investigation focused on a megascale domal relief (Juruá dome) in the Solimões Basin by integrating surface information from remote sensing imagery and subsurface data consisting of magnetic and gravity anomaly maps, well logs and seismic reflection sections. We confirm that the Juruá dome is expressed in the subsurface by a broad growth anticline and related faults, which produced sedimentary units with thickness controlled by the compressive deformation as move away from the dome core. We conclude that this dome reflects a roughly E-W trending maximum compressive horizontal stress active in the late Quaternary, consistent with neotectonic basin inversion by pushes from the Andean Orogeny and movement of the South American plate westward. This deformation promoted strong disturbances in the Amazonian rivers, which changed courses or were strongly recurved in adaptation to the smoothly growing domal relief. The Juruá River valley was entrenched along NE-striking fractures activated by stress-release at the fold axis. This process has contributed to eroding the anticline hinge and lowering its already smooth topography. Central Amazonia contains some of the largest rivers on Earth, thus the present study can contribute to discussions focusing on the influence of folds on the development of existing and past large river systems.

The influence of neotectonic structures on the development of large river valleys is an issue that needs further investigation in various geological settings. Despite the typical low topography, the relief of many areas in central Amazonia was shaped by fault reactivation, but folds have also recently been argued. This work aims to analyze active folding in central Amazonia, determine the regional extent and origin of the compressive stress, and then discuss its control on the development of some large Amazonian rivers. The investigation focused on a megascale domal relief (Juruá dome) in the Solimões Basin by integrating surface information from remote sensing imagery and subsurface data consisting of magnetic and gravity anomaly maps, well logs and seismic reflection sections. We confirm that the Juruá dome is expressed in the subsurface by a broad growth anticline and related faults, which produced sedimentary units with thickness controlled by the compressive deformation as move away from the dome core. We conclude that this dome reflects a roughly E-W trending maximum compressive horizontal stress active in the late Quaternary, consistent with neotectonic basin inversion by pushes from the Andean Orogeny and movement of the South American plate westward. This deformation promoted strong disturbances in the Amazonian rivers, which changed courses or were strongly recurved in adaptation to the smoothly growing domal relief. The Juruá River valley was entrenched along NE-striking fractures activated by stress-release at the fold axis. This process has contributed to eroding the anticline hinge and lowering its already smooth topography. Central Amazonia contains some of the largest rivers on Earth, thus the present study can contribute to discussions focusing on the influence of folds on the development of existing and past large river systems.